System for detecting defective battery packs

ABSTRACT

An electrical cabinet for an uninterruptibe power supply (UPS) system includes universal slots that can receive power modules, battery packs, or chargers. The back plane of the slot has connector terminals for battery packs and power modules. The cabinet can be easily reconfigured as desired by changing the number of power modules chargers or battery packs installed. Circuitry is provided that indicates the capacity and operational readiness of the cabinet. This circuitry monitors the battery packs in each slot, and isolates any detected fault to a particular pack.

The international application was published under PCT Article 21(2) inEnglish.

FIELD OF THE INVENTION

The present invention relates generally to modular uninterruptible powersupply (UPS) systems, and more particularly relates to batterymonitoring systems for use in such UPS systems.

BACKGROUND OF THE INVENTION

Increasingly, businesses, hospitals, utilities, and even consumers arerelying on electronic and computerized equipment to conduct their dailyactivities. Indeed, as we progress through the new economy in theinformation age, the amount of reliance and the required sophisticationof the electonic equipment used will only increase. Unfortunately, suchincreased use and sophistication of the electronic equipment brings anincreased demand for reliable, quality electric power without whichoperations may be disrupted and critical data lost.

Despite the advances in the sophistication and availability ofelectronic and computerized equipment, the availability and reliabilityof high quality electric power and the quantities demanded by thegrowing economy has not kept pace. Indeed, while many utilities believethat rolling brown-outs provide an adequate solution to their inabilityto supply the electric power required by their customers, the impactthat such brown-outs has on a business' productivity and profitabilityis, quite simply, unacceptable.

In addition to the utilities' inability to reliably supply the amount ofelectric power required, the quality of the power that is supplied oftenis so poor so as to affect the operation of the modern sophisticatedelectronic and computer equipment. Voltage sags and spikes arerelatively common on the utility power lines, particularly duringperiods of factory shift changes in industrialized areas. Other powerquality problems may be introduced by natural causes such as lightninginduced voltage spikes, voltage droops caused by accidental contact withpower distribution equipment by animals, tree limbs, etc. Oftentimes,these power quality perturbations have a more detrimental effect on theelectronic and computerized equipment than complete power losses becausethe operating characteristics of the components of such equipmentvaries. That is, some portions of the electronic equipment may ceaseoperating before other portions shut down, possibly resulting inerroneous operation, corrupted data, etc.

To overcome these and other problems resulting from the lack of thequantity and quality of electric power required by the modern electronicand computerized equipment, uninterruptible power supply systems havebeen developed. These systems typically allow the main utility power tosupply the connected load during periods of availability of high qualityutility generated electric power. However, during periods of utilitypower loss or substandard quality, these systems will stop utilizing theutility power input and switch to an alternate source of electric powerto generate the required output for the connected loads. Most often,this alternate source of electric power is from a number of electricstorage batteries. Even in systems that may utilize a motor-drivenelectric power generator, batteries are still typically utilized tobridge the gap between the loss of utility power and the availability ofthe motor-driven generator, which typically requires a finite period oftime after it is started before it is capable of powering the connectedloads. Because the applications vary greatly in their type, size andconfiguration, powering requirements, signal requirements and the like,it will be readily appreciated to those skilled in the art that one sizefits all does not apply and the one size and form of an uninterruptiblesupply systems can not meet the requirements of all applications.Indeed, it is often the case that each application requires asignificantly different configuration of an UPS system.

The two basic components used in UPS systems include battery packs andpower modules. It is also desirable in certain applications to usebattery chargers in the UPS systems. Battery packs have positive andnegative terminals which can be connected together in parallel or seriesto provide the desired combined DC voltage and amperage. Power modulesare much different than battery packs and can serve the purpose ofsignal conditioning and converting DC electrical power into ACelectrical power. Because power modules are typical controlled throughelectronic control signals, power modules must have several inputs andseveral outputs. As such, power modules use much more complex terminalconnectors than battery packs with several input pins and several outputpins.

The electric power storage batteries used in typical uninterruptiblepower supply systems are constructed from a number of individual batterycells that are coupled in series to generate the output voltage requiredfor the system. Since each of the individual battery cells are requiredto generate the proper output voltage, proper operation of each of thebattery cells is paramount to the system's ability to properly supplyquality output power to the connected loads to prevent the problemsdiscussed above. The existence of an undetected failed cell may resultin a system crash during periods of utility power outage when thebatteries are called upon to supply the connected load. Alternatively,the duration or quality of the output power supplied by the system forthe batteries may be greatly reduced, which is also unacceptable from auser standpoint.

To avoid the continued existence of a failed battery cell, some form ofbattery health monitoring for the UPS system is required. Once suchmonitoring system is described in a paper presented at the 13thInternational Telecommunications Energy Conference held in Kyoto, Japan,on Nov. 5–8, 1991 entitled Middle Point Voltage Comparison as a Simpleand Practical but Effective Way to Ensure Battery Systems Capacity toPerform, written by Arto Glad, Pekka Waltari, and Teuvo Suntio. Themonitoring system proposed by this paper uses a voltage signal UWD usedto represent the “middle point” voltage as determined to be the voltagedeviation between a fixed reference voltage and the “middle point”voltage of the battery string. Unfortunately, this paper concludes thatthe battery string must be discharged before “the real anomalies” can bedetected. Specifically, this paper states that the absolute health ofthe batteries can be revealed only by discharging about 70–80% or moreof the batteries' capacity. Likewise, in another paper presented at the18^(th) International Telecommunications Energy Conference on Oct. 6–10,1996, in Boston, Mass., entitled “A Systems Approach to Telecom BatteryMonitoring and Control Using the Rectifier Power Plant” written by KevinE. White, also requires that the battery be discharged significantlybefore the health of the battery may be determined. Indeed, this laterpaper indicates that the float voltage provides no hint of a weakbattery, and requires that all battery testing be performed under load.

While the systems proposed in the above-identified papers may wellprovide adequate monitoring of the health of the batteries, therequirement of discharging 70–80% of the batteries' capacity merely todetermine the health of the batteries carries with it significant risksthat jeopardize the uninterruptible power supply system's ability tosupply the connected load in the event of any utility power failureoccurring during or within a period of several hours after themonitoring has occurred, depending on the ability of the system torecharge the batteries to their full capacity after having beendischarged 70–80%. Further, the complexity of the circuitry required todisable or limit the utility power line input adds significantly to thecost and complexity of such a monitoring system, while reducing theoverall system reliability; a combination which is particularlytroublesome for a system that is meant to increase the reliableoperation of electronic and computer equipment.

Therefore, there is a need in the art for a monitoring system that isable to ensure the health and operability of the batteries utilized inan uninterruptible power supply system without requiring that thesebatteries be discharged during the monitoring operation.

BRIEF SUMMARY OF THE INVENTION

The system of the invention provides a new and improved uninterruptiblepower supply (UPS) system including a modular cabinet or chassisproviding extensibility and reconfigurability of the UPS. Thisextensibility and reconifigurability is made possible through theprovision of common receiving locations in the cabinet or chassisadapted to receive any one of the components of which the UPS iscomprised. Specifically, each receiving location of the modular cabinetor chassis is adapted to receive power modules, battery packs, andbattery chargers. This provides maximum flexibility for the consumer whois now able to fully configure the UPS to his or her own particularneeds, and to fully reconfigure the UPS as his or her needs change, allwithout the necessity of purchasing separate cabinets.

In one embodiment of the invention, an electrical cabinet forconfiguring an uninterruptible power system comprises a plurality ofreceiving locations each adapted to receive either of a power module anda battery pack. In this embodiment, each receiving location includes aterminal connector that includes a power connector adapted toelectrically connect with the battery pack, and a signal connectoradapted to electrically connect with the power module. Further, eachreceiving location preferably includes two separate terminal connectorsarranged in non-interfering locations. Preferably, the signal connectorand the power connector are arranged in a single terminal connectoralong a common strip to which the power modules are adapted to connect.

The electrical cabinet of the invention further comprises partitionsdividing the receiving locations into slots. A user interface is adaptedto provide a status of each receiving location indicative of the use ofthe receiving location. This is aided in one embodiment by the inclusionof sensing circuitry for each receiving location indicating to the userinterface the type of device positioned in the receiving location.

In a further embodiment of the invention, each receiving location isadapted to receive at least two battery packs. In this embodiment, eachreceiving location includes a pair of terminal connectors, one for eachdifferent battery pack. To accommodate the typical inclusion of a fan ineach power module, each receiving location including a vent arranged tobe in close proximity to this fan.

A non-invasive method of monitoring operational readiness of electricpower storage batteries in the uninterruptible power supply (UPS) systemis also presented. The UPS system includes at least one battery channel,each having at least two battery packs coupled in series to supplyoutput power to a connected load. A battery charger is also preferablyincluded to maintain and restore charge to the batteries during normalutility line operation. In this system, the method comprises the stepsof monitoring the voltage at the midpoint between the two battery packsduring a quiescent state of operation of the battery packs. This voltageis compared to a nominal value for the midpoint voltage during thequiescent state of operation, and a lack of operational readiness ofboth battery packs is indicated when the voltage at the midpoint is lessthan the nominal value by a predetermined amount.

In UPS systems having a number of battery channels coupled in parallelwith one another, the step of monitoring comprises the step ofmonitoring a voltage for each of the parallel coupled battery channelsat the midpoint. In such a system, the method further includes the stepsof calculating the nominal value for the midpoint voltage during thequiescent state of operation of the battery packs as the average of thevoltages monitored for each parallel coupled battery channel. A lack ofoperational readiness of a battery channel is then indicated when thevoltage at the midpoint of the battery packs for that channel is lessthan the nominal value by the predetermined amount.

In further embodiment, the method also includes the steps of monitoringthe voltage at the midpoint during float charging of the battery packsand comparing the voltage to a nominal value during the float charging.A lack of operational readiness of one of the two battery packs may thenbe indicated when the voltage at the midpoint varies from this nominalvalue by a predetermined amount. The indication a lack of operationalreadiness may identify one of the two battery packs when the voltage atthe midpoint is greater than the nominal value by the secondpredetermined amount, and the other of the two when the voltage at themidpoint is less than the nominal value by the predetermined amount.

In UPS systems that include a number of battery channels coupled inparallel with one another, an embodiment of the present inventionmonitors the voltage for each of the parallel coupled battery channelsat the midpoint between the two battery packs during the float charging.The method then calculates the nominal value for the midpoint voltageduring the float charging of the battery packs as the average of thevoltages monitored for each parallel coupled battery channel A lack ofoperational readiness of a battery channel is then indicated when thevoltage at the midpoint of the battery packs for that channel variesfrom the nominal value by the predetermined amount. A lack ofoperational readiness of one of the two battery packs of that batterychannel may also be indicated when the voltage at the midpoint isgreater than the nominal value by the predetermined amount, and of theother of the two battery packs when the voltage at the midpoint is lessthan the nominal value by the predetermined amount.

In a further embodiment, the method also includes the steps ofmonitoring the voltage at a midpoint between the two battery packs at astate of discharge of the battery packs, and comparing this voltage to anominal value for the midpoint voltage during the state of discharge. Alack of operational readiness of one of the two battery packs may thenbe indicated when the voltage at the midpoint varies from the nominalvalue by a predetermined amount. A lack of operational readiness of oneof the two battery packs is indicated when the voltage at the midpointis less than the nominal value by the third predetermined amount, and ofa second one of the two battery packs when the voltage at the midpointis greater than the nominal value by the predetermined amount.

In UPS systems including a number of battery channels coupled inparallel with one another, a further embodiment monitors the voltage foreach of the parallel coupled battery channels at the midpoint betweenthe two battery packs during the state of discharge. In this embodiment,the method of the present invention includes the step of calculating thenominal value for the midpoint voltage during the state of discharge asthe average of the voltages monitored for each parallel coupled batterychannel A lack of operational readiness of a battery channel may then beindicated when the voltage at the midpoint of the battery packs for thatchannel varies from the nominal value by the predetermined amount. Alack of operational readiness of one of the two battery packs of thatbattery channel may be indicated when the voltage at the midpoint isless than the nominal value by the predetermined amount, and of theother of the two battery packs of that battery channel when the voltageat the midpoint is greater than the nominal value by the predeterminedamount.

In another embodiment of the present invention, a method of detectingand identifying a failed battery pack in an uninterruptible power supply(UPS) system is also presented. Preferably, the UPS system includes aplurality of parallel connected slots into which may be coupled batterypacks, power modules, or battery chargers as determined and configuredby a user. The slots are adapted to accommodate two battery packs and toprovide a series coupling therebetween. This method comprises the stepsof detecting a presence and type of equipment installed in each slot,monitoring a voltage present at the series coupling between the twobattery packs for each slot into which is installed battery packs,calculating an average midpoint voltage for all slots having batterypacks installed, comparing the voltage for each slot to the averagemidpoint voltage for all slots, and identifying a failed battery packwithin a slot when the voltage for its associated slot deviates from theaverage midpoint voltage by a predetermined amount.

In a further embodiment, the method also includes the steps of comparingthe voltage for each slot to a predetermined expected value, andidentifying a failed battery pack within a slot when the voltage for itsassociated slot deviates from the predetermined expected value by apredetermined amount. Preferably, the method also includes the step ofdetermining an operating mode of the battery packs. In this embodimentthe step of comparing the voltage for each slot to a predeterminedexpected value comprises the step of comparing the voltage for each slotto an operating mode specific predetermined expected value. The step ofidentifying a failed battery pack within a slot may then include thestep of identifying a failed battery pack within a slot when the voltagefor its associated slot deviates from the operating mode specificpredetermined expected value by a predetermined amount.

A system for detecting defective battery packs in a modular, redundantuninterruptible power supply (UPS) system is also presented. Asdiscussed, the UPS system includes a number of parallel connected slotsinto which may be coupled the battery packs, power modules, or batterychargers as determined and configured by a user. Each slot is adapted toaccommodate two battery packs and to provide a series coupling betweenthem. This system comprises a voltage sense circuit coupled to eachseries coupling of each slot. A voltage sense selector circuit iscoupled to each of the voltage sense circuits to selectively enablethem. A controller is coupled to the voltage sense selector circuit tocommand the voltage sense selector circuit to enable a particularvoltage sense circuit for a particular slot. The controller then readsthe voltage sense signal for that particular slot from the voltage sensecircuit. The controller compares the voltage sense signal for theparticular slot to a predetermined expected value. It then identifies anoperational status of the battery packs based on this comparison.

Preferably, the controller reads the voltage sense signal for each slotin which battery packs are installed, calculates an average voltagevalue, and compares the voltage sense signal for each slot to theaverage voltage value to identify the operational status of the batterypacks for each slot. The controller may also read the voltage sensesignal for each slot in which battery packs are installed during a floatcharge mode. It then compares the voltage sense signal for each slot toan expected voltage value for the float charge mode, and identifies oneof the battery packs in a slot as defective when the voltage sensesignal for the associated slot is less than the expected voltage valuefor the float charge mode. The other of the battery packs in a slot isidentified as defective when the voltage sense signal for the associatedslot is greater than the expected voltage value for the float chargemode. The controller also preferably reads the voltage sense signal foreach slot in which battery packs are installed during a discharge mode,compares the voltage sense signal for each slot to an expected voltagevalue for the discharge mode, and identifies one of the battery packs ina slot as defective when the voltage sense signal for the associatedslot is less than the expected voltage value for the discharge mode. Theother one of the battery packs in a slot is identified as defective whenthe voltage sense signal for the associated slot is greater than theexpected voltage value for the discharge mode.

In one embodiment of the present invention, the voltage sense selectorcircuit comprises a shift register having a clock input and a slotselect input from the controller. The shift register sequentiallygenerates a number of output enable signals in response to the clockinput and the slot select input from the controller. Each of the outputenable signals operates to turn on a switching element to connect thevoltage sense circuit to the controller. Preferably, the switchingelement is a metal oxide silicon field effect transistor (MOSFET).

In one embodiment, the electrical cabinet further comprises a supportbase, support bars spaced apart in a rectangular relationship extendingvertically from the support base, side panels extending verticallybetween different pairs of the four support posts, and a number ofshelves extending horizontally between the four support posts. In thisembodiment, the receiving locations are defined between the adjacentshelves. The cabinet further includes a back panel associated with thereceiving locations. The back panel extends generally perpendicular tothe shelves and transversely between the side panels and two of thesupport bars, supporting the terminal connectors. Preferably, theshelves, the side panels, and the support bars are manufactured fromsheet metal material. Pairs of the support bars are further connectedand maintained in spaced relation by a web of sheet metal material.

In an alternate embodiment, an electrical cabinet for configuring anuninterruptible power system with battery packs and modules comprises asupport housing and a number of universal bays defined in the supporthousing and sized to receive either of a battery pack and a powermodule. The electrical cabinet further includes a terminal connector foreach universal bay comprising a power connector adapted to electricallyconnect with the battery pack and a signal connector adapted toelectrically connect with the power module. Preferably, each universalbay includes two terminal connectors arranged in non-interferinglocations. The housing further defines a guide surface for eachuniversal bay. This guide surface is adapted to guide the battery packinto electrical connection with the power connector and the power moduleinto electrical connection with the signal connector. Preferably, eachof the signal and power connectors also include a guide mechanism thatinteracts with a corresponding guide mechanism on either of the batterypack and power module. The guide surface is adapted to first locate thecorresponding guide mechanisms for interaction, and then guide thebattery packs and power modules into electrical connection with thepower connectors and signal connectors, respectively.

In one embodiment, the signal connector and the power connector arearranged in a single terminal connector along a common strip. Further,the power module is adapted to connect to the power connector inaddition to the signal connector. Preferably, the electrical cabinetfurther comprises a user interface adapted to provide a status of eachuniversal bay indicative of the use of the universal bay. Additionally,each universal bay comprises a sensor circuit indicating to the userinterface the type of device positioned in the universal bay.

In an alternate embodiment of the present invention, a back panel foruse in an electrical cabinet of a modular uninterruptible power supply(UPS) system is presented. The UPS is capable of including anycombination or exclusion of battery packs, power modules, and batterychargers within the capacity of the electrical cabinet, which has aplurality of identical receiving locations capable of receiving any oneof the power modules, battery packs, and battery chargers. In thisembodiment of the invention, the back panel comprises a backplane and afirst terminal connector. This terminal connector comprises a powerconnector mounted on the backplane and adapted to electrically connectwith the battery pack, the power module, and the battery charger. Theterminal connector also includes a signal connector mounted on thebackplane and adapted to electrically connect with the power module andthe battery charger.

In one embodiment of the back panel, the backplane comprises a printedcircuit board having power traces and signal traces included therein.These power traces and signal traces are operably coupled to the powerconnector and the signal connector, respectively. Preferably, the backpanel further comprises a second terminal connector positioned in anon-interfering relationship with the first terminal connector. In afurther embodiment, the back panel comprising a guide member rigidlymounted on the backplane. This guide member is adapted to receiveflanges on the battery packs, power modules, and battery chargers toensure proper positioning of the battery packs, power modules, andbattery chargers for engagement with the terminal connector.

In a further alternate embodiment of the present invention, anuninterruptible power system (UPS) comprises an electrical cabinethaving a plurality of universal receiving locations defined therein.These universal receiving locations are adapted to receive battery packsand power modules. The UPS further comprises a power module positionedwithin one of the universal receiving locations and a battery packpositioned within another one of the universal receiving locations.Preferably, the universal receiving locations are further adapted toreceive battery chargers, and the UPS further comprises a batterycharger positioned within a third of the universal receiving locations.Additionally, in one embodiment each of the universal receivinglocations comprises a terminal connector having a power connector and asignal connector positioned to electrically connect with both the powermodule and the battery pack upon insertion.

Other objectives and advantages of the invention will become moreapparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention, andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is an isometric view of an electrical cabinet or chassis forconfiguring and supporting an UPS system, according to an embodiment ofthe present invention;

FIG. 2 is a front view of the electrical cabinet illustrated in FIG. 1;

FIG. 3 is an enlarged fragmentary view of a portion of FIG. 2;

FIG. 4 if an enlarged fragmentary view of a portion of FIG. 2;

FIGS. 5 a and 5 b are rear isometric views of a power module for usewith the electrical cabinet illustrated in FIGS. 1–2;

FIGS. 6 a and 6 b are rear isometric views of an individual battery of abattery pack for use with the electrical cabinet illustrated in FIGS.1–2;

FIG. 7 is a front view of the back panel used in the battery cabinet ofFIG. 1;

FIG. 8 is a side view of the back panel of FIG. 7;

FIG. 9 is an isometric illustration of the back panel of FIG. 7;

FIG. 10 is a rear view of the back panel of FIG. 7;

FIG. 11 is an isometric view of an electrical cabinet or chassis forconfiguring and supporting an UPS system similar to FIG. 1, but with theside panels and back panel removed;

FIG. 12 is a simplified schematic diagram illustrating an embodiment ofthe battery center point sense circuitry in accordance with anembodiment of the present invention;

FIG. 13 is an enlarged, partially fragmentary, isometric view of anelectrical cabinet according to an alternative embodiment of the presentinvention;

FIG. 14 is a isometric view of the rear end of a pair of battery packsadapted to be plugged into the common strip terminal connector of thebattery cabinet shown in FIG. 13; and

FIG. 15 is a isometric view of the rear end of a power module adapted tobe plugged into the common strip terminal connector of the batterycabinet shown in FIG. 13.

While the invention will be described in connection with certainpreferred embodiments, there is no intent to limit it to thoseembodiments. On the contrary, the intent is to cover all alternatives,modifications and equivalents as included within the spirit and scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of illustration, an embodiment of the present invention isdepicted in FIGS. 1 and 2 as a modular chassis or electrical cabinet 20for supporting and organizing battery packs 22 and power modules 24 intoan uninterruptible power supply system (UPS) for such exemplaryapplications as providing power to computer networks, telecommunicationsequipment and any other application where an uninterrupted power sourceis desired. The cabinet 20 is also capable of holding battery chargers23 if desired, which are contained in the same type of drawer supportstructure or module housing 25 as the power modules 24 and plug into theback panel in a similar manner. The module housing 25 slideshorizontally and locks into the inserted position. Further details ofthe module housing 25 and associated locking handle structure aredescribed in U.S. patent application Ser. No. 09/538,056 entitled,“MULTI-FUNCTION HANDLE AND MODULAR CHASSIS INCORPORATING SAME”, assignedto the present assignee, the entire disclosure of which is herebyincorporated by reference.

As illustrated in FIGS. 1 and 2, the cabinet 20 is divided up intoindividual sections 26 to provide a vertical stack. In this embodiment,each section 26 provides three bays or slots 30 for receiving thebattery packs 22 or power modules 24. In this manner, electricalcabinets having only three slots, or alternatively six, nine or twelveor more slots can be readily made utilizing a single size of side panels38. It will be appreciated by those skilled in the art that each sectionneed only have one slot 30, but making each section with multiple slotsis advantageous from practicality and manufacturing standpoints. Otherslot configurations are also possible including side by side horizontalslots as an alternative or in addition to the vertically spaced slots asshown. Each battery pack 22 is housed laterally side by side in theillustrated embodiment such that each battery pack 22 may be insertedseparately, which reduces the exertion of the service technician due tothe typical heavy weight of such battery packs 22. Fewer or more batterypacks may also be provided in other embodiments of the invention.

The power supply cabinet 20 may include a support base 32 upon whichindividual sections 26 can be stacked. The cabinet 20 also includes anouter support housing which can be built out of various materials suchas plastic, sheet metal, metal, structural foam, and other similarmaterials. In the illustrated embodiment, the housing includes a metalframe comprising vertical corner support bars 34 built initially on thesupport base 32. Referring to FIG. 11, adjacent vertical support bars 34standing vertically upright from the cabinet 20 are connected and spacedapart by a web 35 of sheet metal material near the top and bottom of thesupport bars 34. Pairs of vertical support bars 34 are stamped andformed from a common sheet of metal. The vertical corner support bars 34are covered by a front panel (not shown), a back panel 40, and sidepanels 38. The vertical height of the support bars 34 is determined bythe number of bays desired and determines the number of sections 26provided, e.g. 3, 6, 9, or 12. A top 42 that includes a user interface43 including a display 45 extends across the top of the front panel,back panel 48 and side panel 38. In the illustrated embodiment thepanels 38, 40 are formed of sheet metal, however other material may beused as previously indicated.

The side panels 38 and back panel 40 also include vents 44 for coolingpurposes thereby preventing overheating of a UPS when in use. In thedescribed embodiment and referring to FIG. 2, the vents 44 in the backpanel 40 are all along the left hand side of the back panel 40 andrecessed a couple of inches rearward from an interior surface 49 toreceive rearwardly projecting fans 70 (FIG. 5 a, 5 b) of the powermodules 24. In this manner, fans are positioned in close proximity withthe vents 44 to facilitate cooling of the power modules 24.

To provide the individual slots 30, individual shelves 28 extendinghorizontally are supported in parallel, vertically spaced apartrelationship. Like the side and back panels 38, 40, the shelves 28 canbe readily formed from sheet metal. The corners of the shelves 28 aresnapped in, mounted, fastened or otherwise secured to the verticalsupport bars 34. The shelves 28 also include generally flat andgenerally smooth top surfaces 46 which allows battery packs 23 or powermodules 24 to easily slide into and out of the slots 30. The uppersurface of the support base 32 can also provide the first shelf 33, i.e.the bottom surface of the lower most slot 30. A plastic center rail 47snaps into the center of each shelf 28 and extends rearwardly.Referring, also, now to FIG. 4, each center rail 47 provides beveledinner guide surfaces 51 that slide against corresponding inner beveledguide surfaces 55 of each battery pack 22 to align the battery packs 22in the proper position for plugging into their respective terminals.Referring, also, now to FIG. 3, the housing 25 of power modules andbattery chargers includes an elongate groove 29 that rides over the rail47. The shelf 28 above each slot 30 includes a downward depending flange57 on both side ends that provides parallel outer guide surfaces 59. Theouter guide surfaces 59 engage and slide against both the outer surfacesof the battery packs 22 and power modules 24 as shown in FIGS. 3 and 4to align the battery packs 22 and power modules 24 in the properposition for plugging into their respective terminals. Referring toFIGS. 6 a and 6 b, the battery packs 22 also include a beveled surface61 that guides and eases insertion into the slots 30 against the outerguide surfaces 59.

In accordance with the present invention, the slots 30 are universal,readily capable of having either the power modules 24 or the two batterypacks 22 inserted and plugged-in or otherwise electrically connected tothe cabinet 20. In the described embodiment, different terminalconnector locations have been selected for the battery packs 22 and thepower modules 24 such that the locations of the respective terminals ineach slot 30 do not interfere with one another. The battery packs 22 areapproximately one-half the width of the power modules 24. The powermodule 24 and the two side by side battery packs 22 are sized closelyand just smaller than the size of the slots 30 such that theysubstantially fill the slot and substantially align to plug into therespective terminal connectors on the back 49 of each slot. Thus, it isnot only the cabinet 20 which is novel, but, also, the battery packs 22and power modules 24 that are also novel by virtue of their similarsizes and the selected non-interfering locations of the respectiveterminal connectors.

Referring to FIG. 3, it can be seen that the back 49 of each slot 30includes separate power module plug-in connectors 50 and batteryterminal plug-in connectors 52 at different locations. Each battery pack22 includes a positive and negative terminal 54, 56 in the form ofprojecting prongs or posts (FIGS. 6 a and 6 b). Since, in theillustrated embodiment, each slot 30 may accommodate two battery packs22, the back 49 of each slot 30 includes two sets of battery terminalplug-in connectors 52 in the form of positive and negative electricalsockets 58, 60 positioned to align with positive and negative terminals54, 56 for interfitting and electrically connecting with the positiveand negative terminals 54, 56. Referring to FIG. 3, one of the batteryterminal plug-in connectors 52 is located proximate the horizontalcenter of the slot 30 while the other battery terminal plug-in connector52 is located proximate the right end of the slot 30. The plug-inconnectors for the battery packs 22 are known as power connectors asthey provide the raw power source or supply for the UPS system.

Similarly, the power module plug-in connectors 50 of the back panel 40are positioned to connect with corresponding plug-in connectors 51 onthe rear face of the power modules 24 (FIGS. 5 a and 5 b). The powermodule plug-in connectors 50 are provided horizontally proximate thebottom of the back surface 49 between the pair of battery terminalplug-in connectors 52. Each power module plug-in connector 50 includesmultiple pin sized sockets 62 for interfitting and electricallycontacting corresponding interfitting projecting pins 64 arranged inseparate terminal connectors 51 on the back surface of the power module24. The number of pins 64 allow for a variety of inputs, outputs andcontrol of the power module 24 or are otherwise necessary for carryinglarge quantities of electrical power. In particular, the single terminalconnector shown on the right hand side in FIG. 5 a is a signal connector51 b and carries electronic control signals for controlling theoperational output of the power module 24. The signal connector 51 bplugs into a corresponding signal connector 50 b (see FIG. 7) on theback panel 40. In contrast, the four other terminal connectors 51 arepower connectors 51 a that receive the raw electrical power from thebattery packs 22 and also output conditioned power for use. The powerconnectors 51 a connect with corresponding power connectors 50 a on theinterior surface 49 of the back panel 40. The power module plug-inconnectors 50 and battery terminal plug-in connectors 52 also do notinterfere with the vents 44 and fans 70 which are aligned along the lefthand side.

The slots 30 are universal and each can receive either a power module 24or a battery pack 22 as desired to better meet the powering requirementsof a particular application. No changes need to be made to the cabinet20 to switch the number of power modules 24 or battery packs 22 so longas the total does not exceed the numbered slots 30. The full capacity ofthe cabinet 20 can be utilized before another cabinet 20 is required.The end user is able to add additional battery packs 22 or power modules24 or switch locations of battery packs 22 and power modules 24 asdesired without concern as to whether a slot 30 is dedicated to receiveeither a battery pack or power module.

All of the plug-connectors 50, 52 are provided on a single back panel 40that provides an electrical circuit connecting the various slots 30 inan operative manner. The back panel 40 of each section 26 is illustratedin FIG. 10 including a printed circuit board “back plane” in whichtraces 63 are etched on the back and front sides of a substrate board65. Traces 63 include signal traces 63 b and power traces 63 a. Thenarrower signal traces 63 b are electrically connected with sockets ofsignal connectors 50 b and carry electronic control signals to the powermodules 24. The wider power traces 63 a are electrically connected withsockets of the power connectors 50 a and carry the primary electricalpower outputs of the battery packs 22 into the power modules 24 and alsooutput the conditioned electrical power for usage. It will beappreciated by those skilled in the art that discrete wires may be usedas an alternative to traces 63. The substrate board 65 supports theplug-in connectors 50 a–b, 52 on the interior side of the back panel 40as illustrated in FIGS. 7 and 9 (a side view of back panel 40 isillustrated in FIG. 8). The plug-in connectors 50 a–b, 52 areelectrically coupled to the traces 63 in an operative manner.

Guide mechanisms are also provided to precisely align the respectiveplug-in connectors of the battery packs 22 and the power modules 24 withthe back panel 40. The guide mechanism for guiding the connection of thepower modules 24 is illustrated in FIG. 5 a and takes the form ofrearwardly-extending plastic flanges 66 on the power modules 24 thatco-act with corresponding structure on the back panel 40. The plasticflanges 66 have beveled guide surfaces 67 that engage the corners 69(See FIG. 9) of receiving slots 71 defined on a plastic guide member 73of the back panel 40 which is rigidly mounted on an interior facing sideof the substrate board 65. The beveled guide surfaces 67 contact thecorners 69 to adjust the position of the power module 24 slightly toensure that the pins 64 are properly received into the sockets 62.

As illustrated in FIGS. 6 a and 6 b, the guide mechanism for guiding theconnection of each battery pack 22 takes the form of an outer plasticguard 75 surrounding the positive and negative terminals 54, 56 thatco-acts with and fits over a corresponding plastic guard 77 on theplastic guide member 73 of the back panel 40. The plastic guard 77 onthe plastic guide member 73 includes beveled guide surfaces 79 thatcontact the corresponding guard 75 to adjust the position of the batterypack 22 slightly to ensure that the positive and negative terminals 54,56 are properly received into the positive and negative sockets 58, 60.

The controller of the user interface 43 electronically polls each bay orslot 30 to determine whether a battery pack 22, a power module 24 orother device is provided in each of the slots 30. In the describedembodiment the controller 43 measures electrical activity, such as thelocation of the voltage in each slot 30. For example, if electricalactivity is sensed at the power module plug-in connectors 50 of aparticular slot 30, then the controller 43 determines that a powermodule 24 is present in that slot 30. Similarly, if electrical activityis sensed associated with the battery terminal plug-in connectors 52 ina particular slot 30, then the controller 43 determines that a batterymodule 22 is present in that slot 30. The controller 43 can also detectand indicate whether there are any defects of the power module 24 orbattery packs 22 by comparing sensed voltages or electrical signals tostored normal operating ranges, thereby providing an early warning to aUPS system maintenance technician. The polling is conducted at timedintervals such that the system automatically refreshes to reflect newinformation as power modules 24 or battery packs 22 are pulled orswitched. Other sensor mechanisms can also be used, such as usingindicator pins in the connectors to indicate a particular type ofplug-in module. Such information can be gathered with the controller 43and viewed on the display 45.

In one embodiment, a system for detecting defective battery packs in themodular, redundant uninterruptible power supply (UPS) system utilizes asingle analog sense input 80 into microcontroller 43 as illustrated inFIG. 12. One skilled in the art will recognize, however, that individualanalog sense inputs may be used as desired. The sense lines 82 _(a-c)coupled to each of the battery center tap points on the back plane areselectively coupled to the single analog sense input 80 to allow themicrocontroller 43 to sequentially monitor the voltage at each of thesepoints. The selection circuitry in this embodiment includes a shiftregister 84 that sequentially enables an electronic switch, such asMOSFET 86 _(a-c) to couple each of the sense lines 82 _(a-c) to thesingle analog sense input 80. The shift register 84 operates incombination with a clock input 88 and a slot select input 90 frommicrocontroller 43. In this embodiment, a module send input 92 _(a-c) isalso included to allow the microcontroller 43 to distinguish differenttypes of modules that may occupy the individual slots, as will bedescribed more fully below.

In the embodiment of the battery monitoring system of FIG. 12, themicrocontroller 43 first establishes a baseline (all zeroes) position byclocking the shift register through its total cycle, e.g., 16 or moreclock cycles for a typical shift register. Once this baseline all zerosposition has been established, the microcontroller 43 sets the slotselect line 90 high for one clock cycle. This causes shift register 84to enable the first switch 86 _(a) to couple the sense line 82 _(a) tothe analog sense input 80. The microcontroller 43 is then to sense thevoltage at the battery center tap for this slot. Once this reading hasbeen recorded, the slot select line 90 is taken low, and the shiftregister 84 is again clocked so that the next slot may be monitored whenthe slot select line 90 is again taken high. In this way, each of theindividual slots will be polled by the microcontroller 43 in thissequential fashion. At each clock, the voltage on analog sense inputwill indicate the condition of the battery center tap for each of thesubsequent slots.

As described above, the modular UPS chassis allows the installation ofdifferent types of modules therein. Specifically, each slot mayaccommodate a pair of battery packs, or a power module or batterycharger. In a situation where a power module is installed in a slot, thevoltage reading at the battery center tap sense line 82 for thatparticular slot will read zero. To allow the microcontroller 43 todifferentiate this condition from a condition where batteries areinstalled but are inoperative, each slot also includes a module sendinput 92 _(a-c) as introduced above. In one embodiment of the presentinvention, the power modules and battery chargers will output a squarewave on this module send line 92 to indicate their presence in the slot.During polling operation as the shift register 84 sequences to the slothaving the power module installed therein, when shift register 84enables the electronic switch, e.g., 86 _(a), the square wave on modulesend line 92 _(a) will result in the electronic switch 86 _(a) beingturned on and off at the rate of the square wave. In this way, themicrocontroller 43 can detect that a power module is installed in thatparticular slot.

In a preferred embodiment, the square wave is generated at a relativelyslow frequency, e.g., one-tenth the clock rate. The microcontroller 43is then able to detect the square wave by virtue of changes from zero to5 volts every 10^(th) cycle to thereby “decide” that a power module isinstalled in this location. As an alternative to detecting the presenceof a module, an additional signal “module send” could be sent to themodule. If a module is present in that location, the module will send aformatted CAN signal to the interconnect board letting it know itssystem address. Interconnect board knows which slot the module is insince it counts the number of clock pulses sent out. If at any givendata shift there is no CAN message or insufficient DC voltage is fedback, the system recognizes that the slot is empty.

Through the use of this system, the microcontroller 43 monitors thevoltage at the center point of the two battery packs in each individualslot. As each pack is normally 60 volts in a typical UPS system, thenominal voltage at the battery center tap is 60 volts. Under normaloperating conditions, this point will always be about one-half the totalstring voltage. During float charge operation during which the charge oneach of the individual cells in the battery pack reaches approximately2.47 volts, the center point is then increased to a nominal ofapproximately 74.1 volts (in a system having 30 cells per battery pack).At a low battery discharge point during load each cell may be reduced toapproximately 1.75 volts, which therefore lowers the center point toapproximately 52.5 volts under this operating condition. As thesevoltages are obviously greater than may be handled by a typicalmicrocontroller 43, the individual voltage sense from each slot isdivided down to a level safe for the microcontroller 43. In theembodiment illustrated in FIG. 12, the voltage input is scaled by one MΩand a 63.4 kΩ resistor, and clamped by a Zener diode to a safe level toprotect the microcontroller 43 from an overvoltage condition.

In operation, the microcontroller 43 polls each of the (3, 6, 9, or 12)slots in turn as discussed above. Initially, the microcontroller 43 will“learn” each position's nominal voltage, which will vary slightly due toresistor and battery pack tolerances. Primarily, the microcontroller 43looks for consistency among the battery pairs in each slot. If anysingle slot varies by more than a predetermined amount from the otherslots, the microcontroller 43 will flag that slot as having a problem.This consistency among the battery packs installed in the slots ischecked during each of the various operating conditions. Nominally, themicrocontroller 43 expects to see a voltage of approximately 3.58 voltsin a quiescent state, 4.42 volts during a float charge mode, 3.13 voltsduring low battery discharge under load, and 0.0 volts when no batteriesare installed in the slot. A typical variation in these values may belimited to approximately 1% upon proper selection of sensing components,although larger tolerance variations may be accommodated as needed. Avariation from these numbers by more than a predetermined amount, e.g.by approximately 5% or more, will indicate that one or both of thebatteries in the slot has failed. The individual readings from each ofthe individual slots are compared against the nominal values expectedfor each operating condition, and/or are compared against an averagevoltage value calculated from the voltage readings from all of the slotshaving batteries installed therein.

How the system reacts under different fault conditions allows themicrocontroller 43 to detect which battery pack in a particular slot isdefective. Recognizing that batteries typically fail high impedance(open cell, dry, or sulfated) different voltage readings duringparticular modes of operation may be used to identify which of the twobattery packs in a particular slot is failed. For example, themicrocontroller 43 will expect to see a nominal voltage during aquiescent mode of 3.58 volts when the “bottom” battery pack has failedopen. With this same failure, a voltage of 5.10 volts (corresponding tothe Zener clamping voltage) will be expected during the float chargemode of operation, and a voltage of 2.68 volts will be expected when thebottom battery pack is open during a low battery discharge under loadcondition. The “top” battery pack being failed open will result in anominal voltage of 3.58 volts to be seen by the microcontroller 43during all modes of operation. If both battery packs are failed open, orif no battery packs are properly installed in a particular slot, themicrocontroller 43 will expect to see a voltage of zero volts. With thisinformation, the microcontroller 43 can detect a defective battery bycomparing the sensed voltages at the battery center tap either againstthemselves or a known nominal value. In this way, the operationalreadiness or lack thereof of the battery packs installed in each slotsmay be indicated.

An alternative embodiment of the present invention is illustrated inFIGS. 13–15 as a battery cabinet 100 having a single strip terminalconnector 102 on a panel 103. Except for the configuration of the singlestrip terminal connector 102, the second embodiment is the same as thefirst embodiment. The single strip terminal connector 102 is adapted toplug into both battery packs 104 and power modules 106 and includes bothsignal connectors and power connectors. The power modules 106 includemetal prongs 108 and pins 109 that plug into prong receiving sockets 110and pin receiving sockets 111, respectively. The pins 109 act as signalconnectors and transmit electronic control signals while the prongs 108act as electrical power connectors and transmit the raw and/orconditioned electrical power. Each battery pack 104 also includes twoprongs 114 that plug into two of the same prong receiving sockets 110 asfor the power modules to provide the raw electrical power to the system.As such, two of the four prong receiving sockets 110 on each side of theterminal connector 102 are used for both battery packs and powermodules.

All of the references cited herein, including patents, patentapplications, and publications, are hereby incorporated in theirentireties by reference.

The foregoing description of various embodiments of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the preciseembodiments disclosed. Numerous modifications or variations are possiblein light of the above teachings. The embodiments discussed were chosenand described to provide the best illustration of the principles of theinvention and its practical application to thereby enable one ofordinary skill in the art to utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such modifications and variations arewithin the scope of the invention as determined by the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally, and equitably entitled.

1. A non-invasive method of monitoring operational readiness of electricpower storage batteries in an uninterruptible power supply (UPS) system,the UPS system having at least one battery channel, each having at leasttwo battery packs coupled in series to supply output power to aconnected load and a battery charger to maintain and restore charge tothe batteries during normal utility line operation, comprising the stepsof: monitoring a voltage at a midpoint between the two battery packsduring a quiescent state of operation of the battery packs; comparingthe voltage to a first nominal value for the midpoint voltage during thequiescent state of operation of the battery packs; indicating a lack ofoperational readiness of both battery packs when the voltage at themidpoint is less than the first nominal value by a first predeterminedamount.
 2. The method of claim 1, wherein the UPS system includes aplurality of battery channels coupled in parallel with one another, andwherein the step of monitoring comprises the step of monitoring avoltage for each of the parallel coupled battery channels at a midpointbetween the two battery packs during a quiescent state of operation, themethod further comprising the steps of: calculating the first nominalvalue for the midpoint voltage during the quiescent state of operationof the battery packs as the average of the voltages monitored for eachparallel coupled battery channel; and indicating a lack of operationalreadiness of a battery channel when the voltage at the midpoint of thebattery packs for that channel is less than the first nominal value bythe first predetermined amount.
 3. The method of claim 1, furthercomprising the steps of: monitoring the voltage at a midpoint betweenthe two battery packs during float charging of the battery packs;comparing the voltage to a second nominal value for the midpoint voltageduring the float charging of the battery packs; indicating a lack ofoperational readiness of one of the two battery packs when the voltageat the midpoint varies from the second nominal value by a secondpredetermined amount.
 4. The method of claim 3, wherein the step ofindicating a lack of operational readiness of one of the two batterypacks comprises the step of indicating a lack of operational readinessof a first one of the two battery packs when the voltage at the midpointis greater than the second nominal value by the second predeterminedamount.
 5. The method of claim 3, wherein the step of indicating a lackof operational readiness of one of the two battery packs comprises thestep of indicating a lack of operational readiness of a second one ofthe two battery packs when the voltage at the midpoint is less than thesecond nominal value by the second predetermined amount.
 6. The methodof claim 3, wherein the UPS system includes a plurality of batterychannels coupled in parallel with one another, and wherein the step ofmonitoring comprises the step of monitoring a voltage for each of theparallel coupled battery channels at a midpoint between the two batterypacks during the float charging, the method further comprising the stepsof: calculating the second nominal value for the midpoint voltage duringthe float charging of the battery packs as the average of the voltagesmonitored for each parallel coupled battery channel; and indicating alack of operational readiness of a battery channel when the voltage atthe midpoint of the battery packs for that channel varies from thesecond nominal value by the second predetermined amount.
 7. The methodof claim 6, wherein the step of indicating a lack of operationalreadiness of a battery channel comprises the step of indicating a lackof operational readiness of a first one of the two battery packs of thatbattery channel when the voltage at the midpoint is greater than thesecond nominal value by the second predetermined amount.
 8. The methodof claim 6, wherein the step of indicating a lack of operationalreadiness of a battery channel comprises the step of indicating a lackof operational readiness of a second one of the two battery packs ofthat battery channel when the voltage at the midpoint is less than thesecond nominal value by the second predetermined amount.
 9. The methodof claim 1, further comprising the steps of: monitoring the voltage at amidpoint between the two battery packs at a state of discharge of thebattery packs; comparing the voltage to a third nominal value for themidpoint voltage during the state of discharge of the battery packs;indicating a lack of operational readiness of one of the two batterypacks when the voltage at the midpoint varies from the third nominalvalue by a third predetermined amount.
 10. The method of claim 9,wherein the step of indicating a lack of operational readiness of one ofthe two battery packs comprises the step of indicating a lack ofoperational readiness of a first one of the two battery packs when thevoltage at the midpoint is less than the third nominal value by thethird predetermined amount.
 11. The method of claim 9, wherein the stepof indicating a lack of operational readiness of one of the two batterypacks comprises the step of indicating a lack of operational readinessof a second one of the two battery packs when the voltage at themidpoint is greater than the third nominal value by the thirdpredetermined amount.
 12. The method of claim 9, wherein the UPS systemincludes a plurality of battery channels coupled in parallel with oneanother, and wherein the step of monitoring comprises the step ofmonitoring a voltage for each of the parallel coupled battery channelsat a midpoint between the two battery packs during the state ofdischarge, the method further comprising the steps of: calculating thethird nominal value for the midpoint voltage during the state ofdischarge of the battery packs as the average of the voltages monitoredfor each parallel coupled battery channel; and indicating a lack ofoperational readiness of a battery channel when the voltage at themidpoint of the battery packs for that channel varies from the thirdnominal value by the third predetermined amount.
 13. The method of claim12, wherein the step of indicating a lack of operational readiness of abattery channel comprises the step of indicating a lack of operationalreadiness of a first one of the two battery packs of that batterychannel when the voltage at the midpoint is less than the third nominalvalue by the third predetermined amount.
 14. The method of claim 12,wherein the step of indicating a lack of operational readiness of abattery channel comprises the step of indicating a lack of operationalreadiness of a second one of the two battery packs of that batterychannel when the voltage at the midpoint is greater than the thirdnominal value by the third predetermined amount.
 15. A method ofdetecting and identifying a failed battery pack in an uninterruptiblepower supply (UPS) system, the UPS system having a plurality of parallelconnected slots into which may be coupled battery packs, power modules,or battery chargers as determined and configured by a user, the slotsbeing adapted to accommodate two battery packs and providing a seriescoupling therebetween, the method comprising the steps of: detecting apresence and type of equipment installed in each slot; monitoring avoltage present at the series coupling between the two battery packs foreach slot into which is installed battery packs; calculating an averagemidpoint voltage for all slots having battery packs installed therein;comparing the voltage for each slot to the average midpoint voltage forall slots; and identifying a failed battery pack within a slot when thevoltage for its associated slot deviates from the average midpointvoltage by a predetermined amount.
 16. The method of claim 15, furthercomprising the steps of: comparing the voltage for each slot to apredetermined expected value; and identifying a failed battery packwithin a slot when the voltage for its associated slot deviates from thepredetermined expected value by a predetermined amount.
 17. The methodof claim 16, further comprising the step of determining an operatingmode of the battery packs, and wherein the step of comparing the voltagefor each slot to the predetermined expected value comprises the step ofcomparing the voltage for each slot to an operating mode specificpredetermined expected value, and wherein the step of identifying afailed battery pack within a slot when the voltage for its associatedslot deviates from the predetermined expected value by the predeterminedamount comprises the step of identifying a failed battery pack within aslot when the voltage for its associated slot deviates from theoperating mode specific predetermined expected value by thepredetermined amount.
 18. The method of claim 17, wherein the step ofdetermining an operating mode of the battery packs determines that thebattery packs are operating in a quiescent mode, and wherein the step ofidentifying a failed battery pack within a slot comprises the step ofidentifying both battery packs as failed when the voltage for theirassociated slot is less than a first predetermined value by a firstpredetermined amount.
 19. The method of claim 17, wherein the step ofdetermining an operating mode of the battery packs determines that thebattery packs are operating in a float charging mode, and wherein thestep of identifying a failed battery pack within a slot comprises thestep of identifying a first one of the two battery packs within the slotas failed when the voltage for its associated slot is less than a secondpredetermined value by a second predetermined amount, and identifying asecond one of the two battery packs within the slot as failed when thevoltage for its associated slot is greater than a third predeterminedvalue by a third predetermined amount.
 20. The method of claim 17,wherein the step of determining an operating mode of the battery packsdetermines that the battery packs are operating in a discharging mode,and wherein the step of identifying a failed battery pack within a slotcomprises the step of identifying a first one of the two battery packswithin the slot as failed when the voltage for its associated slot isless than a fourth predetermined value by a fourth predetermined amount,and identifying a second one of the two battery packs within the slot asfailed when the voltage for its associated slot is greater than a fifthpredetermined value by a fifth predetermined amount.
 21. The method ofclaim 15, wherein the step of detecting a presence and type of equipmentinstalled in each slot comprises the step of polling each slot for anequipment type identifier.
 22. A system for detecting defective batterypacks in a modular, redundant uninterruptible power supply (UPS) system,the UPS system having a plurality of parallel connected slots into whichmay be coupled the battery packs, power modules, or battery chargers asdetermined and configured by a user, each slot being adapted toaccommodate two battery packs and to provide a series couplingtherebetween, the system comprising: a voltage sense circuit coupled toeach series coupling of each slot and operable to generate a voltagesense signal in response to a voltage present thereon; a voltage senseselector circuit coupled to each of the voltage sense circuits, thevoltage sense selector circuit operable to selectively enable thevoltage sense circuits; a controller operably coupled to the voltagesense selector circuit to command the voltage sense selector circuit toenable of a particular voltage sense circuit for a particular slot, thecontroller reading the voltage sense signal for the particular slot fromthe voltage sense circuit; and wherein said controller compares thevoltage sense signal for the particular slot to a predetermined expectedvalue and identifies an operational status of the battery packs basedthereon.
 23. The system of claim 22, wherein the controller reads thevoltage sense signal for each slot in which battery packs are installed,calculates an average voltage value, and compares the voltage sensesignal for each slot to the average voltage value to identify theoperational status of the battery packs for each slot.
 24. The system ofclaim 23, wherein the controller reads the voltage sense signal for eachslot in which battery packs are installed during a float charge mode,compares the voltage sense signal for each slot to an expected voltagevalue for the float charge mode, and identifies a first one of thebattery packs in a slot as defective when the voltage sense signal foran associated slot is less than the expected voltage value for the floatcharge mode, and identifies a second one of the battery packs in a slotas defective when the voltage sense signal for the associated slot isgreater than the expected voltage value for the float charge mode. 25.The system of claim 23, wherein the controller reads the voltage sensesignal for each slot in which battery packs are installed during adischarge mode, compares the voltage sense signal for each slot to anexpected voltage value for the discharge mode, and identifies a firstone of the battery packs in a slot as defective when the voltage sensesignal for an associated slot is less than the expected voltage valuefor the discharge mode, and identifies a second one of the battery packsin a slot as defective when the voltage sense signal for the associatedslot is greater than the expected voltage value for the discharge mode.26. The system of claim 22, wherein the voltage sense selector circuitcomprises a shift register having a clock input and a slot select inputfrom the controller, the shift register sequentially generating aplurality of output enable signals in response to the clock input andthe slot select input from the controller, each of the output enablesignals operative to turn on a switching element to connect the voltagesense circuit to the controller.
 27. The system of claim 26, wherein theswitching element is a metal oxide silicon field effect transistor(MOSFET).